As data transmission service demands increase, interconnection between integrated circuit (IC) chips becomes increasingly important. A level conversion circuit needs to be connected between different chips, to implement digital signal level conversion between the different chips.
FIG. 1 is a schematic circuit diagram of a digital signal input circuit. It can be learned from a circuit 100 shown in FIG. 1 that a digital signal is inputted from a digital input (DI) port, and is inputted into an isolating circuit 110 after voltage division by means of a resistor R1 and a resistor R2. A light emitting diode 120 in the isolating circuit determines whether a level of the digital signal is a high level or a low level. Finally, the level of the digital signal is converted, using a pull-up resistor R3, into a level that can be supported by a target chip. The converted digital signal is outputted from a digital output (DO) port, and is inputted into the target chip. In the circuit 100, the light emitting diode in the isolating circuit determines whether the level of the digital signal is a high level or a low level. However, precision of determining a level by a light emitting diode is relatively low, and a conversion error easily occurs when a level of a digital signal is converted.